-LRB- CNN -RRB- -- When Lukas Hartmann , 29 , signed up for 23andMe 's at-home genetic testing service , there were no surprises in his results .

The Berliner learned he would probably die from `` a mix of heart attack and prostate cancer , '' he wrote on a friend 's blog , but `` nothing special there . ''

Then a few months ago , he received an update from the company .

Hartmann 's genetic code showed two mutations that are linked to limb-girdle muscular dystrophy , he says the site told him . `` Some people with limb-girdle muscular dystrophy lose the ability to walk and suffer from serious disability , '' his results page read .

This ca n't be true , he thought . It must be an error .

Genetic testing can be a powerful tool . It can offer information about your family history , tell you how your body might respond to different drugs and identify your risk factors for disease .

It can also be misleading .

The Food and Drug Administration on Monday ordered 23andMe to stop sales of its $ 99 home genetic testing kits , saying the Google-backed company has not proven the validity of its product .

The FDA warned that customers who received inaccurate results could suffer from undue mental anguish or undergo unnecessary medical procedures . The government agency has asked 23andMe to revise its marketing strategy to comply with federal regulations .

The action triggered outrage among some of 23andMe 's supporters .

`` So GMOs , aspartame , artificial flavors & colors , pink slime ... no problem ! '' a poster named Laura Ann wrote on the company 's Facebook page . `` But in no way should we be allowed the right to know our own genetic material as a means for making better decisions about our health . ''

In a statement , 23andMe said it has received the FDA 's letter and will be working to address the agency 's concerns .

There are more than 3 billion letters in our genetic code . Though it 's been 10 years since the Human Genome Project was completed , scientists still do n't understand what every gene does , and what a mutation might mean for someone 's health .

It 's one of the issues opponents to home genetic testing kits raise most often . If DNA experts do n't understand 100 % what a gene mutation means , how can we expect consumers to ?

5 cool things DNA testing can do

Scientists have identified more than 2,000 single gene disorders , says Rebecca Nagy , president of the National Society of Genetic Counselors . These are disorders that can be diagnosed based on the mutation of a single gene in the body ; some examples include Huntington 's disease or cystic fibrosis .

But conditions such as Type 2 diabetes or Alzheimer 's are more complex . Hundreds of genes may contribute to the development of these diseases , Nagy says , and a person 's risk is also influenced by his or her environment . Testing for markers of risk scattered across someone 's genome is `` really only testing for the tip of the iceberg . ''

`` That 's where it gets a little scary , because if a person has a normal test result on 23andMe , they leave thinking they do n't have a risk , '' she says . `` It 's not that the science behind -LRB- this kind of genetic testing -RRB- is n't good . It 's that the science behind them is n't complete . ''

The upside of these at-home genetic testing kits -- and 23andMe is n't the only company that sells them -- is that they 've generated a lot of buzz about genetics , Nagy says . She says she believes most early adopters of the tests are information-savvy and understand the results are n't set in stone .

`` I do n't think that anyone thinks that this kit replaces formal testing by a doctor , '' Heather Armstrong posted on 23andMe 's Facebook page . `` I seriously doubt that a doctor would agree to perform , say , a double mastectomy , based on these results . ''

Joseph Stolarski posted , `` If you find something interesting , you then take it to a medical professional for further evaluation . No one is or should rely on it for medical ` diagnosis . ' It 's just a tool , like personally checking your heart rate with a watch or checking your weight on a scale . ''

But Nagy says she worries about what will happen when the tests become more mainstream .

Giving this kind of information to someone unfamiliar with genetic testing 's limitations could prove dangerous .

Nagy recommends anyone who wants to do genetic testing first talk to a genetic counselor . Counselors have specialized graduate degrees and extensive knowledge of the human genome . They 're also trained in explaining test results to laymen .

`` Our message is to be a smart consumer , '' Nagy says . `` Know what you 're doing so that when you get the results back you can really use them to your best benefit . ''

Hartmann did some intense investigating , saying he looked at the raw data 23andMe provided him . He eventually found he did indeed have two mutations , he says , but they were n't on the same gene . He says he submitted his `` bug report '' to the company and it apologized .

In general , Hartmann thinks it 's a good thing for every person to have affordable access to his or her genetic data . But he 's browsed the community forums on 23andMe . com and has seen how seriously some people take their results -- without fully understanding them .

Hartmann says he now believes he will not get limb-girdle muscular dystrophy , although he says there is a risk he could pass the genetic mutations onto his kids .

`` I can live with that , '' he wrote . `` For quite some time , I hope . ''

Parents push for standardized screening of Jewish genetic diseases

CNN 's Dorrine Mendoza and CNNMoney 's James O'Toole and Aaron Smith contributed to this report .

@highlight

FDA has ordered 23andMe to stop sales of its $ 99 home genetic testing kits

@highlight

23andMe supporters took to social media to protest the FDA 's decision

@highlight

Genetic testing can be a powerful tool if used correctly , experts say